Repo created

libs/coding/file_reader.hpp

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+#pragma once
+
+#include "coding/reader.hpp"
+
+#include "base/base.hpp"
+
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+#include <string>
+
+// FileReader, cheap to copy, not thread safe.
+// It is assumed that file is not modified during FireReader lifetime,
+// because of caching and assumption that Size() is constant.
+class FileReader : public ModelReader
+{
+public:
+  static uint32_t const kDefaultLogPageSize;
+  static uint32_t const kDefaultLogPageCount;
+
+  explicit FileReader(std::string const & fileName);
+  FileReader(std::string const & fileName, uint32_t logPageSize, uint32_t logPageCount);
+
+  // Reader overrides:
+  uint64_t Size() const override { return m_size; }
+  void Read(uint64_t pos, void * p, size_t size) const override;
+  std::unique_ptr<Reader> CreateSubReader(uint64_t pos, uint64_t size) const override;
+
+  FileReader SubReader(uint64_t pos, uint64_t size) const;
+  uint64_t GetOffset() const { return m_offset; }
+
+protected:
+  // Used in special derived readers.
+  void SetOffsetAndSize(uint64_t offset, uint64_t size);
+
+private:
+  class FileReaderData;
+
+  FileReader(FileReader const & reader, uint64_t offset, uint64_t size, uint32_t logPageSize, uint32_t logPageCount);
+
+  // Throws an exception if a (pos, size) read would result in an out-of-bounds access.
+  void CheckPosAndSize(uint64_t pos, uint64_t size) const;
+
+  uint32_t m_logPageSize;
+  uint32_t m_logPageCount;
+  std::shared_ptr<FileReaderData> m_fileData;
+  uint64_t m_offset;
+  uint64_t m_size;
+};